GSAP > Draggable 0.7.0 update

This isn't an update of the main GSAP files, but rather an update to a minor utility (Draggable) so I didn't think I should create a new tag and new directory, etc. - is that okay? Let me know if I should do something differently or if the package.json file has to be updated to a different version or something (although that'd be odd because the TweenMax.min.js file hasn't been updated). 

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- Added new "trigger" functionality for defining a child element that serves as the initiator of dragging.

- Worked around several bugs in the stock browser of several Android devices.

- Improved performance by shifting rendering from mousemove/touchmove event handlers to the main requestAnimationFrame loop that drives GSAP.

- Improved algorithm for sensing the velocity of the user's mouse/touch.

- Fixed an issue that caused an error when the Draggable JS file was loaded BEFORE the <body> tag was declared.